1. Field of the Invention
The present invention relates in general to transmissions of wheeled motor vehicles, and more particularly to the transmissions of a semi-automatic type which provides the transmission with a synchronized gear change operation by the work of an electromagnetic multiple disc clutch.
2. Description of Related Art
In order to clarify the task of the present invention, transmissions shown in Japanese Patent Second Provisional Publication (Tokkou-sho) 54-28894 and Japanese Patent First Provisional Publication (Tokkai-hei) 5-99333 will be briefly described in the following.
In the former publication, there is shown a so-called constantly gear meshed transmission equipped with a synchronizing system which is provided at one end of a countershaft of the transmission. A first gear tightly disposed on an output shaft is constantly meshed with a second gear which is rotatably disposed on the countershaft. The synchronizing system is constructed to decelerate or accelerate the second gear to establish rotation synchronization of the two shafts before a selected dog clutch effects engagement of a corresponding speed gear with the output shaft.
In the latter publication, there is shown another constantly gear meshed transmission equipped with a synchronizing system which is constructed to establish a rotation synchronization of the countershaft and output shaft (viz., main shaft) only in the lowest and highest gear changes. More specifically, only the dog clutches for the lowest and highest operation gear speeds are equipped with a synchronizing mechanism.
However, due to the following reasons, the transmissions of the above-mentioned publications have failed to provide users or car makers with a satisfaction.
That is, in the transmission of former publication, the synchronizing system provided at one end of the countershaft induces enlargement of the transmission in an axial direction and increase in weight of the transmission, which inevitably bring about a difficulty with which the transmission is mounted onto a given limited space of the vehicle body.
While, in the transmission of latter publication, when a gear change other than the lowest and highest gear changes is needed, the synchronizing mechanism of either one of the dog clutches for the lowest and highest operational gear speeds has to be indirectly used, which however increases the time needed for establishing the rotation synchronization between the countershaft and the output shaft. If the needed time for the synchronization is excessively large, an engine roar tends to occur.
In general, the manual transmissions of the above-mentioned constantly gear meshed type are equipped with a dry type clutch for connecting the transmission input shaft with an output member of the engine, and the dry type clutch is actuated by a hydraulic actuator. Thus, operation of the clutch (viz., engagement/disengagement operation) is inevitably affected by a temperature of hydraulic oil in the actuator and by a surge pressure appearing upon engagement of the clutch, which tends to make a responsive operation of the clutch difficult.
Accordingly, it is an object of the present invention to provide a semi-automatic transmission which is free of the above-mentioned shortcomings.
According to a first aspect of the present invention, there is provided a semi-automatic transmission which comprises an input shaft; a countershaft; constantly meshed gears arranged between the input shaft and the countershaft; an electrically controlled dog clutch operatively disposed on one the input shaft and the countershaft, the dog clutch being of a type free of a synchronizing mechanism and fastening one of the meshed gears to a corresponding one of the input shaft and the countershaft when operated, thereby to establish a given torque transmission path from the input shaft to the countershaft; a control unit which controls the dog clutch in accordance with information signals applied thereto; and an electromagnetic multiple disc clutch having an input part adapted to be driven by an engine and an output part connected to the input shaft.
According to a second aspect of the present invention, there is provided a semi-automatic transmission which comprises an input shaft having a first group of gears rotatably disposed thereon; a countershaft having a second group of gears tightly disposed thereon, said second group of gears being constantly and respectively engaged with said first group of gears; an electrically controlled dog clutch operatively disposed on said input shaft, said dog clutch functioning to fasten one of said first group of gears to said input shaft when operated; an electromagnetic multiple disc clutch having an input part adapted to be driven by an engine and an output part connected to said input shaft; and a control unit which controls both said dog clutch and said electromagnetic multiple disc clutch upon receiving a gear change instruction.
According to a third aspect of the present invention, there is provided a semi-automatic transmission which comprises an input shaft having a first group of gears rotatably disposed thereon and a third group of gears tightly disposed thereon; a countershaft having a second group of gears tightly disposed thereon and a fourth group of gears rotatably disposed thereon, the second and fourth groups of gears being constantly and respectively engaged with the first and third groups of gears; an electrically controlled first dog clutch operatively disposed on the input shaft, the first dog clutch functioning to fasten one of the first group of gears to the input shaft when operated; an electrically controlled second dog clutch operatively disposed on the countershaft, the second dog clutch functioning to fasten one of the third group of gears to the countershaft when operated; a wet type electromagnetic multiple disc clutch having an input part adapted to be driven by an engine and an output part connected to the input shaft; and a control unit which controls the first and second dog clutches and the electromagnetic multiple disc clutch upon receiving a gear change instruction, wherein the wet type electromagnetic multiple disc clutch comprises an input drum adapted to be driven by the engine; an input clutch hub connected to the input shaft to rotate therewith; an annular main clutch selectively assuming an engine condition wherein the input drum and the input clutch hub are engaged and a disengaged condition wherein the input drum and the input clutch hub are disengaged; an annular pilot clutch which selectively assumes an engaged condition and a disengaged condition; and an annular cam mechanism which forces the annular main clutch to assume the engaged condition when the annular pilot clutch assumes the engaged condition, wherein the annular pilot clutch and the annular cam mechanism are concentrically received within the annular main clutch with respect to an axis of the input shaft.